With the increase in the amount of transmission information and in the variety of functions, a large number of electronic devices and the like recently having been used are configured such that an optical element including a light source such as a vertical-cavity surface-emitting laser (VCSEL), that converts electrical signals into optical signals, a photodetector such as a photodiode that converts optical signals into electrical signals, and the like is mounted on an electric wiring board, and such that an optical interconnect line such as an optical waveguide is combined with the optical element. With the decrease in the size of electronic devices and the like, the decrease in the size of wiring boards and the increase in the degree of integration thereof have been required, and flexible wiring boards that can be mounted in a limited space have been desired. An example of such flexible opto-electric hybrid boards has a configuration as shown in FIG. 7 (see PTL 1, for example). In this opto-electric hybrid board, an electrical interconnect line 3 including an electrically conductive pattern is provided on the front surface of an insulation layer 1 made of polyimide and the like, and part of the electrical interconnect line 3 serves as a pad 3a. The pad 3a is covered with a gold plated layer 4, and an optical element 5 is mounted on the gold plated layer 4. A predetermined part of the electrical interconnect line 3 which is closer to an end of the insulation layer 1 is similarly covered with the gold plated layer 4 to serve as a connector pad part 6 for external electrical connection. The electrical interconnect line 3 except the pad 3a and the connector pad part 6 is covered with a coverlay 7, and is insulated and protected by the coverlay 7.
An optical waveguide W including an under cladding layer 9, a core 10, and an over cladding layer 11 is provided on the back surface (surface opposite from the surface where the electrical interconnect line 3 is formed) of the insulation layer 1. This optical waveguide W includes a mirror part 12 that reflects light to couple the optical axis of light L passing through the core 10 and the optical axis of the optical element 5 mounted on the front surface of the insulation layer 1. A reinforcement layer 13 made of metal, resin and the like is provided on the back surface of the insulation layer 1, with an adhesive layer 14 therebetween, to prevent an excessive force from being applied to the periphery of the portion mounted with the optical element 5 during handling.